The present invention relates to a clamping apparatus for a tiebarless injection moulding machine.
Tiebarless injection moulding machines offer better access to the moulding tool, and thereby facilitate and reduce the set up time of the machine each time the moulding tool is changed. Of course, as a tiebarless moulding machine does not have tiebars to absorb the huge forces transmitted to the platens and moulding tool during a moulding process it is imperative to have a properly designed mechanism to absorb the forces. In this respect, it is necessary that the two mould halves forming the moulding tool remain accurately aligned with each other whilst the two halves are pressed together and under application of high pressure.
Several attempts have been made to provide a tiebarless injection moulding machine which is able to deal with the clamping forces in a satisfactory manner.
U.S. Pat. No. 5,354,196 describes a clamping apparatus for a tiebarless injection moulding machine having a machine frame, the clamping apparatus comprising a fixed platen fixed to the machine frame, a movable platen supported by said machine frame, drive means for moving said movable platen towards and away from said fixed platen, and a clamping structure for maintaining the fixed and movable platens in a clamping position, wherein, in the clamping position of the fixed and movable platens, a respective part of the clamping structure is in force transmitting relationship with each of the fixed and movable platens such that the clamping structure is able to absorb clamping forces.
In the arrangement of U.S. Pat. No. 5,354,196 the clamping structure absorbs the clamping forces, whereby the base machine frame is kept from bending, and whereby a tight fit between the two platens is ensured. The arrangement provides a double structure in which the machine frame is isolated from the deforming effects of the clamping forces. Transmission of the clamping forces to the platens is achieved by way of pivotal joints.
However, the structure of U.S. Pat. No. 5,354,196 is somewhat complex and presents a number of practical limitations. Most notably, it has been found difficult to provide pivotal joints which can reliably transmit the huge clamping forces required, whilst preserving the rotational freedom required between the machine frame and the clamping structure.